Several important mechanical properties can be read from a material's stress–strain behaviour, but they describe different things.

Strength

Yield strength characterizes the stress at which significant plastic deformation begins. Ultimate strength is the maximum engineering stress reached during the test.

Strength therefore describes how much stress a material can withstand under a specified loading mode.

Ductility

Ductility describes how much plastic deformation a material can undergo before fracture. A ductile material can reach large strains; a brittle material fractures after relatively little plastic deformation.

Toughness

Toughness describes the energy a material can absorb per unit volume before fracture. It corresponds to the area under the stress–strain curve up to fracture.

A material can be strong but brittle, or ductile but relatively weak. High toughness generally requires a useful combination of strength and ductility.

Resilience

Resilience is the energy absorbed per unit volume while deformation remains elastic. It corresponds to the elastic portion of the area under the stress–strain curve.